The control of temperature and humidity in circulating air frequently involves the use of air washers for treating the air. The air washer is usually operated so that air leaving the air washer is cooled nearly to saturation at the required supply air dew point. When the cooling load of the comfort zone or work space being conditioned is less than the design load, the nearly saturated air is then reheated to the temperature required prior to delivery to the comfort zone or work space. Such an arrangement is wasteful of energy in that air recirculated from the comfort zone or work space involves energy usage for both the cooling and reheating treatments. The energy waste in this system can be reduced by employing a bypass which allows a portion of the return air to bypass the air washer spray section so that it does not undergo the cooling treatment. A bypass arrangement, however, is limited to approximately 30% of the return air because the resulting reduced air velocity of the remaining portion of the air stream passing through the air washer renders the moisture eliminator associated with the air washer less effective.
An alternative to the air washer bypass has been described wherein energy savings are realized by maintaining a non-saturated condition in the air leaving the air washer and the water spray in the air washer is modulated in response to the dry bulb temperature of the conditioned comfort zone or work space. This alternative reduces operating costs by eliminating a substantial proportion of the reheat requirements.
Another energy-saving arrangement which has been investigated involves a variable air volume conditioning system. Such systems are generally used in situations where temperature control in the conditioned comfort zone is of primary interest and the humidity control is not critical. Variable air volume systems are particularly attractive for installations having a number of comfort zones with different heating and cooling demands. These systems conserve energy by redistributing heating and cooling loads in the various comfort zones and by operating at reduced capacity during periods of low demand.